In a first step, a torque requested by a user is determined and modified in subsequent steps by different functions which reproduce the effects of at least one independently determined usage and/or operating parameter of the internal combustion engine on the torque actually produced by same, so that at the end of the sequence of steps the target torque required during the operation of the internal combustion engine is established and the operation of the internal combustion engine and the determination of the at least one usage and operating parameter are monitored for errors. If errors occur, diagnostic values describing or indicating said errors are generated and the diagnostic values are used to modify, in particular limit, the target torque.
In vehicles having internal combustion engines as drive units, the internal combustion engines are controlled by means of complex monitoring and control methods. For example, the driver's torque request as measured by the accelerator pedal position or rather its rate of change is taken into account in the control of the internal combustion engine.
For internal combustion engines in the prior art, a target torque is determined which the internal combustion engine must provide during operation. Particularly in the case of internal combustion engines used as the source of propulsion for a vehicle, this involves what is known as torque management, which comprises the steps described in the introduction. Once the target torque is established, it is implemented by means of fixed engine-type-dependent conversion into control variables, such as a quantity of fuel to be injected. The advantage of this approach is that individual characteristics of the internal combustion engine only need to be taken into account in the final step.
In addition, however, so-called diagnostic procedures are carried out which determine the state of usage and/or operating parameters of the internal combustion engine, such as the useful life of the motor oil, the exhaust gas properties, the engine speed, the cooling water temperature, etc. If on the basis of such a diagnostic procedure an operating situation of the internal combustion engine is detected which could be detrimental to the service life of the internal combustion engine, the exhaust gas behavior, the fuel consumption or taking other aspects into account, then on the basis of the diagnostic procedure the quantity of fuel injected into the internal combustion engine will be reduced. The same applies if an error occurs. Thus in many driving conditions a safety-relevant or even safety-critical situation may arise if, for example, reducing the quantity of fuel injected causes a reduction in engine speed or torque during an overtaking maneuver, resulting in less powerful acceleration or even deceleration of the vehicle. Since the driver of the vehicle does not expect the reduction in torque and is reliant on the availability of acceleration especially when overtaking, weaker acceleration may have safety implications.
Since sources of error are themselves mainly engine-specific, the prior art intervenes to take account of diagnosed problems or abnormalities only after the target torque has been determined. Said target torque is then suitably limited before it is converted into engine-specific control parameters, thereby ensuring that malfunctions or other prevailing circumstances are appropriately taken into account. One prevailing circumstance which has long been taken into account in this way is the sooting behavior of an internal combustion engine, particularly in the case of an internal combustion engine with internal mixture formation. Here the target torque, once determined using the above-mentioned steps, is possibly reduced such that the internal combustion engine has a desired exhaust gas behavior, in particular a desired particle or soot emission. Subsequent to such exhaust-gas-relevant limiting strategies, in the past more far-reaching prevailing circumstances were also taken into account, e.g. a maximum torque to be handled by a transmission downstream of the internal combustion engine, a maximum motor oil or cooling water temperature, etc., by suitably limiting the target torque determined using the steps described or if necessary reducing it.
However, this procedure may bring about the safety-critical situations likewise described in the introduction.